Terahertz (THz) radiation is of great interest for imaging science and technology applications, with potentially great promise for homeland security, medical imaging, and defense imaging applications, among others. With their high sensitivity and selectivity, THz systems can be used to monitor public facilities, high-occupancy buildings, and even the open air for toxic industrial chemicals, chemical agents, biological agents, and trace explosives in a continuous and autonomous manner. Because of its superior penetration through many materials relative to other types of radiation, THz radiation is particularly well-suited for the detection and imaging of chemical and biological weapons concealed under clothing. In addition, wavelengths in the THz range may resonate with many biological molecules, including strands of DNA, in a unique manner. As a result, THz sources may also be used as sensors for the early detection of bioaerosols such as spores, bacteria, viruses, and pathogens. Unfortunately, the lack of sufficiently powerful, compact sources and detectors in the 0.3 to 30 THz range has drastically limited the development of THz sources for use in these fields.
The large second-order nonlinearities inherent in LiNbO3 and its sister ferroelectrics, together with the ability to quasi-phase match pumps and products, make these materials ideal candidates for optically pumped terahertz generation via difference frequency mixing (DFM) or optical rectification (OR). The major drawback of these materials is that, unpumped, they absorb strongly (α˜25 cm−1) in the THz regime. As a consequence, conventional THz generation has been limited either to surface interactions by way of reflection or diffraction, or to bulk interactions through thin (˜1 mm thick) samples.